Abnormal proliferation of the epidermis is associated with cumulative unprotected exposure to ultraviolet radiation leading to the accumulation of somatic mutations. Recent research has shown that mitochondria not only play an important role in providing cellular energy, but also may have a central role in apoptosis and neoplasia. There are now several reports of mitochondrial genes that were previously thought to function only in energy production that have not been shown to be mutated in familiar tumor syndromes, and reports of acquired homoplasmic mitochondrial DNA (mtDNA) mutations in human tumors. This proposal seeks to test the role of mtDNA changes in the process of photoaging and aberrant keratinocyte hyperplasia. First, ultraviolet radiation will be used to induce photodamage and tumor production in the hairless mouse. The mtDNA will be studied from photodamaged skin and from benign and malignant epidermal neoplasms to determine the types of somatic mtDNA mutations in photodamaged mouse skin. Next, mtDNA mutations will be recovered from hyperproliferating keratinocytes by isolation of mitochondria and fusion into fibroblast cells that lack their own mtDNA to create cytoplasmic hybrid (cybrid) libraries. Individual cybrid clones will be screened for mtDNA mutations and the effect of these DNA changes will be analyzed. The cybrids will be studied for alterations in oxidative phosphorylation biochemistry and ATP production, as well as for alterations in cellular phenotype including growth characteristics, matrix metalloproteinases expression, ability to escape apoptosis, and ability to form tumors. The ability of mutant mtDNAs to become dominant over wild type will also be studied genetically in fusion assays. Finally, recovered mtDNA mutations will be returned to the live epidermis by the generation of transmitochondrial transgenic mice to study the ability of these mutations to alter growth and tumor development in the intact mouse epidermis. [unreadable] [unreadable] [unreadable]